1. Field of the Invention
The present invention relates to a luminescent diode (LED) that improves rightness uniformity. The present invention also relates to a fabrication method of the LED and a backlight assembly having the LED.
2. Discussion of the Related Art
Data processors have been recently developed to have various shapes, various functions and higher data-processing speed. Because the data processed in the data processor is in the form of an electrical signal, a display device is needed to check the data processed in the data processor.
Display devices include flat panel display devices. A liquid crystal display (LCD) device is a type of flat panel display device. An LCD device displays images using liquid crystal. LCD devices are advantageous in industrial fields because they are thin, light, consume low power and have a low operational voltage.
In most cases, LCD devices are configured to include a liquid crystal panel that displays images and a backlight assembly that supplies light to the liquid crystal panel.
A light source in the backlight assembly may use electro-luminescence (EL), a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent lamp (HCFL), a luminescent diode (LED), etc.
A backlight assembly including a CCFL is problematic because mercury contained in the lamp bonds easily with metal to form an amalgam. This shortens the lifetime of the lamp. Moreover, the backlight assembly including the CCFL has shortcomings. For example, as temperature varies, the brightness of the assembly may vary severely. Also, it is problematic to dispose of mercury, a virulently poisonous heavy metal.
However, backlight assemblies including an LED do not have these shortcomings. Therefore, backlight assembly including an LED have been developed.
An LED includes a point light source, which may be configured with a plurality of LEDs emitting red, green and/or blue light, or a plurality of LEDs emitting white light. Backlight assemblies including LEDs have a smaller size than other backlight assemblies and are able to better maintain light uniformity. Thus, these backlight assemblies are high-brightness backlight assemblies.
LCD devices may be classified into two types according to the arrangement of the light source. The two types are an edge type LCD device and a direct type LCD device. In an edge type LCD device, the backlight assembly includes a light source on a side surface of the LCD device and a light guide plate that guides light emitted from the LED towards the front of the LCD device. The light guide plate is disposed behind a liquid crystal panel. In a direct type LCD device, the backlight assembly includes a plurality of light sources behind a liquid crystal panel. The light emitted from the plurality of light sources is directly irradiated on the liquid crystal panel which is disposed in front of the plurality of light sources.
A related art LCD will be illustrated with reference to the accompanying drawings.
FIG. 1 is an exploded perspective view of a related art edge type LCD device.
Referring to FIG. 1, the backlight assembly 20 includes a bottom case 90, a plurality of LEDs 60, a printed circuit board (PCB) 61 that supplies power to the LEDs 60, a housing 62 that protects the LEDs 60, a light guide plate 50 that converts light generated from the LEDs 60 into a surface light source, and optical sheets 30. The plurality of LEDs 60 may be disposed on a side surface of the bottom case 90 such that they are spaced apart by a predetermined distance. The plurality of LEDs 60 emit light. In addition, the optical sheets 30 are disposed over the light guide plate 50 and aid in diffusing and condensing light.
The backlight assembly 20 may further include a reflective plate 70 that may be attached or coated on the bottom case 90.
The plurality of LEDs 60 emit light when power is supplied by the PCB 61. The light emitted from the plurality of LEDs 60 is inputted into and guided through the light guide plate 50 so that it is irradiated frontward towards a liquid crystal panel 10 disposed in front of the light guide plate 50.
FIG. 2 is an enlarged perspective view of an LED 60 of the related art edge type LCD device.
Referring to FIG. 2, a related art LED 60 has predetermined radiation angles with respect to X-X′ and Y-Y′ axes based on a reference point. A radiation angle refers to a maximum angle of emitted light. The related art LED 60 may have predetermined radiation angles of about 110° with respect to the X-X′ and Y-Y′ axes based on the reference point.
The related art LED 60 is a point light source having an emitting area less than that of a CCFL. Thus, the related art LED 60 may be slim and is therefore easily applied in small-sized edge type LCD devices.
FIG. 3 is a schematic view illustrating external defects of the related art edge type LCD device.
Referring to FIG. 3, the related art LCD device includes a liquid crystal panel 10, a top case 11 that protects the liquid crystal panel 10, and a plurality of LEDs 60 disposed on one side surface of the LCD device. The plurality of LEDs 60 supply light to the liquid crystal panel 10.
In the related art LCD device, because the radiation angle of an LED 60 is about 110°, a bright portion A and a dark portion B are formed in regions in a side of the liquid crystal panel 10 corresponding to regions where the plurality of LEDs 60 are disposed.
As shown, bright portions A and dark portions B are alternately repeated in a predetermined region of the liquid crystal panel 10. This causes the brightness of the LCD device to become non-uniform. These non-uniformities cause hot spots. The bright portion A corresponds to a region within the radiation angle (about 110°) of the light emitted from the LED 60. The dark portion B corresponds to a region outside of the radiation angle (about 110°) of the light emitted from the LED 60. Hot spots are external defects in LCD devices and therefore, result in reduced LCD device production yields.